Electromagnetic induction revealed by MESSENGER's vector magnetic data: The size of Mercury's core

• Published in: Icarus Vol. 354; p. 114112
• Main Authors: Katsura, Taka’aki, Shimizu, Hisayoshi, Momoki, Naoya, Toh, Hiroaki
• Format: Journal Article
• Language: English; Japanese
• Published: Elsevier Inc 15.01.2021; Elsevier BV
• Subjects: Magnetic fields; Magnetospheres; Mercury, interior; Magnetic fields; Magnetospheres; Mercury, interior
• ISSN: 0019-1035; 1090-2643
• DOI: 10.1016/j.icarus.2020.114112

Gauss coefficients of Mercury's internal/external magnetic field with high time resolution are essential to delineate electrical properties within Mercury. Although the time-averaged structure of Mercury's magnetic field has been studied so far, its time variation has been less studied using the observed data directly. Here we determined the annual and semi-annual variations of Mercury's external magnetic field in Mercury Year as the characteristic periods that contribute to electromagnetic (EM) induction by converting the magnetopause-crossing data of MESSENGER into the subsolar distance. We obtained the time series of Mercury's internal Gauss coefficients by spherical harmonic analyses of MESSENGER's vector magnetic data using a series of constrained inversions. In the inversions, we used KT14 model as a function of the subsolar distance to estimate the external magnetic field at desired moments. Finally, we estimated the core radius of Mercury as 2011 ± 180 km from the inductive response of the annual variation. •The internal Gauss coefficients of Mercury were derived explicitly.•The principal variation of the Hermean magnetopause is subject to not synodic but annual change.•The annual variation yielded internal to external Gauss coefficient ratios supporting a very large metallic core of Mercury.